We are studying the in vitro patterns of sensitivity of human tumors, particularly ovarian and testicular cancer, to antineoplastic agents and the mechanisms of resistance to antineoplastic drugs. Drug sensitivity studies are performed using: 1) a clonogenic assay in fresh human tumor specimens, 2) established tissue culture lines of human tumors, and 3) in selected murine neoplasms. These studies have provided a rationale for new therapeutic approaches in ovarian cancer and have aided in the selection of chemotherapy for individual patients. The mechanisms for drug resistance are being examined at the cellular level in fresh human tumor cell suspensions and in established cell lines.